Unlike Dudley, he took the side of the Parliament, and joined their army, in which he served for some time as a soldier.

His zeal and abilities commended him to his officers, and he was raised from one position to another, until in the course of a few years we find him holding the rank of captain.

"While a soldier," says he, "I had sometimes the honour and misfortune to lodge and dislodge an army;" but this is all the information he gives us of his military career.

In the year 1648 he was instrumental in discovering and frustrating a design on the part of the Royalists to seize Doyley House in the county of Hereford, and other strongholds, for which he received the thanks of Parliament "for his ingenuity, discretion, and valour," and a substantial reward of 500L.[3] He was also recommended to the Committee of Worcester for further employment.
But from that time we hear no more of him in connection with the civil wars.

When Cromwell assumed the supreme control of affairs, Yarranton retired from the army with most of the Presbyterians, and devoted himself to industrial pursuits.
We then find him engaged in carrying on the manufacture of iron at Ashley, near Bewdley, in Worcestershire.